the surge protector handles 15amp @ 125 volt ac, which is what every normal house outlet holds (an AC outlets is usually 20amps. I run me a special circuit that send 30amp @ 125 volt, But I have a Pro poweramp that produce 2600 watt RMS, plus a few other thing). an 15amp surge protect is good for 1850watts continous power. a 18 amps 12volts circuit is equal to about 100watts and that is not even continous watts, but the process is actually more complicated than that as your Ac convertor in your psu uses even more watts

but you will be ok. you won't even be close to do any damage

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you psu rating is the draw from your computer, so a 550 watt power supply will either draw 550 max or 550 continous (depend on maker) which translte to about 5 amps . the would be the max that any 1 computer would pull by itself. the other accessories will equal about 100-500 more watts, so you will be ok with a 15 amp surge protector

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